Metal anodes of valve metals such as titanium, tantalum, or niobium, or alloys thereof having electrocatalytic coatings of platinum metals, platinum metal oxides, mixtures of valve metal oxides or other oxides with platinum metal oxides, and so-called mixed crystal material for use in electrolytic processes have been of much interest in recent years. By "valve metal" is meant a metal or alloy which, when connected as an anode in an electrolyte and under the conditions in which the metal or the alloy is subsequently to operate as an anode, exhibits the phenomenon that within a few seconds of the passage of the electrolysis current drops to less than 1% of the original value.
By "electrocatalytic coating" is meant a coating material applied to the metal base of the electrode, which will conduct an electrical current from the metal base to the electrolyte, and which will catalyze an electrochemical reaction at the surface of the electrode. Such a catalytic coating will prevent the passivation of a valve metal electrode base when it is used as an anode.
Valve metal anodes which include a noble metal or mixed metal oxide electrocatalytic coating are used in cathodic protection. Such materials, particularly with the coating, are expensive and somewhat difficult to fabricate. Such coated metals come in a variety of forms such as tubes, bars, ribbons, wires, or expanded mesh. Expanded mesh is now employed in steel reinforced concrete systems as well as other applications. The mesh is formed from expanded sheet and then coated and coiled into rolls for applications to a concrete deck. An example is seen in Bennett et al U.S. Pat. No. 4,900,410. The individual strands of such mesh are relatively small and subject to breakage. Because of the roll set the mesh won't readily lay flat. It has to be cut with tin snips and the rough and jagged edges present a fabricators nightmare.
Relatively small wire is much more readily fabricated, but may not have the capacity, strength or provide the redundancy desired for a system of long life and effectiveness. Larger wires can be used, but then are difficult to form or fabricate into an anode system. A wire anode system for tank bottoms may be seen in U.S. patent application Ser. No. 08/007,537, filed Jan. 22, 1993, now U.S. Pat. No. 5,340,455, entitled CATHODIC PROTECTION SYSTEM FOR ABOVE GROUND STORAGE TANK BOTTOMS AND METHOD OF INSTALLING.
It would therefore be desirable to have an anode having the characteristics of relatively small wire, but the capacity of larger wire, bar, or ribbon. It is also desirable that a low cost anode be highly flexible and easily coiled, yet not require a straightener. More importantly, it is important that the anode be available in continuous lengths, easily fabricated and electrically connected to itself and to power sources and not have the characteristics of coiled cut mesh strips.